The present invention relates to turbine casing alignment and, more particularly, to an alignment tool and method that refines and simplifies turbine shell alignment and achieves additional degrees of freedom control in alignment.
The annular gap between a turbine case and rotating blade airfoil tip in a turbine is called ‘clearance.’ Leakage of pressurized gases through this gap reduces efficiency. On the other hand, if the rotor contacts the stator, the result could be catastrophic. It is important to have positive and minimal clearance for enhanced efficiency. Uniform clearance about the circumference of the rotor is needed in order to effectively minimize the clearance. If the rotor and casing are eccentric, the clearance varies along the circumference and is difficult to control. See FIG. 1. In addition to making the casing and rotor concentric, they should also be aligned such that their axes are co-linear. See FIG. 2. It would thus be desirable to devise a tool and simplified method that will achieve this function.
Existing designs for this purpose typically lack multiple degrees of freedom to control both co-linearity and concentricity. As a consequence, ‘out-of-plane’ misalignment may occur resulting in the elliptical clearance shown in FIG. 2.